Zoom and focus control method and system

ABSTRACT

A focus lens and a zoom lens group having a first zoom lens and a second zoom lens are controlled separately from one another in an internal-focus camera. The positions of the focus lens and the second zoom lens in the zoom lens group are tracked, and are controlled to approach no closer to one another than a minimum safe distance to avert collisions between the focus lens and the second zoom lens.

CROSS-REFERENCE

[0001] The present invention is related to subject matter disclosed inthe following co-pending patent applications:

[0002] 1. United States patent application entitled, “Zoom and FocusControl System in an Optical System” (HP Docket No. 10006922-1), namingGregory V. Hofer, David K. Campbell, Masahiro Ohno, and YoshihiroYamazaki as inventors and filed on even date herewith; and

[0003] 2. United States patent application entitled, “Brightness Controlfor Auto-Focus in an Optical System” (HP Docket No. 10006923-1), namingGregory V. Hofer, David K. Campbell, Masahiro Ohno, and YoshihiroYamazaki as inventors and filed on even date herewith.

FIELD OF THE INVENTION

[0004] This invention relates to photography, and more particularly to amethod for controlling photographic lenses.

BACKGROUND

[0005] An internal-focus lens group is often used in a camera to reducethe size and weight of the overall lens. Referring to FIG. 1, a standardinternal-focus lens 100 is shown. The mechanism or mechanisms for movingthe lenses, as well as any control electronics, are not shown forclarity. The internal-focus lens 100 includes a number of other lenses,including a focus lens 102, which itself can include one or moreelements. The focus lens 102 can move between a rear focusing position120 to focus on an object at infinity and a front focusing position 122to perform macro focusing. Macro focusing is typically utilized when aphotographer wishes to focus on an object located particularly close tothe camera itself. In one embodiment, the focus lens 102 focuses animage on an image detector 130 such as a charge-coupled device (CCD), orphotographic film. In another embodiment, the image detector 130 is notused, and the focus lens 102 creates an image that can be viewed withthe human eye. In such an embodiment, the lens 100 may be used in abinocular or telescope device, or other type of viewing device. Theinternal-focus lens 100 can include a single zoom lens adapted to moverelative to the focus lens 102, or a zoom lens group 104 having a firstzoom lens 106 and a second zoom lens 108 adapted to move relative to oneanother and the focus lens 102. Each zoom lens 106, 108 can include oneor more elements. By moving the zoom lenses 106, 108 relative to oneanother along the optical axis 110, the degree of magnification can becontrolled. When the zoom lenses 106, 108 are close together, they arein a telephoto position where a greater degree of magnification isprovided. When the zoom lenses 106, 108 are further apart, they are in awide-angle position where a lesser degree of magnification is provided.The second zoom lens 108 moves forward to a front zoom position 124 whenthe zoom lenses 106, 108 are closest together for the greatestmagnification, and moves backward to a rear zoom position 126 when thezoom lenses 106, 108 are furthest apart for the greatest wide angleview.

[0006] In order to save space within a camera, the front focusingposition 122 of the focus lens 102 may be located in front of the rearzoom position 126 of the second zoom lens 108. Thus, the focus lens 102can collide with the second zoom lens 108 within a potential collisionzone 128 between the front focusing position 122 and the rear zoomposition 126. Such a collision can damage the focus lens 102 and/or thesecond zoom lens 108. During normal operation of the camera, the focuslens 102 and the second zoom lens 108 typically will not collide, as themacro feature is rarely used in normal operation, and it is usually usedwhen the zoom lens group 104 is in telephoto position. However, even asingle collision between the focus lens 102 and the second zoom lens 108can ruin those lenses, requiring the user to repair them at someexpense, or discard the camera altogether.

SUMMARY

[0007] A focus lens and a zoom lens group are controlled in an internalfocus camera to maintain a minimum safe distance between the focus lensand an adjacent zoom lens.

[0008] In one aspect of the invention, the focus lens and a zoom lensgroup having a first zoom lens and a second zoom lens are controlledseparately from one another.

[0009] In another aspect of the invention, the positions of the focuslens and the second zoom lens in the zoom lens group are tracked.

[0010] In another aspect of the invention, the focus lens and the secondzoom lens are controlled to approach no closer to one another than aminimum safe distance. In this way, collision between the focus lens andthe second zoom lens is prevented, thereby preventing damage to thelenses.

[0011] The invention will be more fully understood upon consideration ofthe detailed description below, taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic view of the lens configuration of a priorart camera, showing the zone in which a focus lens can collide with azoom lens.

[0013]FIG. 2 is a block diagram of a camera.

[0014]FIG. 3 is a flow chart of a method for providing a minimum safedistance between the focus lens and a zoom lens.

[0015]FIG. 4 is a schematic view of a lens configuration within thecamera, where the lenses are configured in a telephoto mode.

[0016]FIG. 5 is a schematic view of a lens configuration within thecamera, where the lenses are configured in a wide-angle mode.

[0017] Use of the same reference symbols in different figures indicatessimilar or identical items.

DETAILED DESCRIPTION

[0018] Referring to FIG. 2, a block diagram of a camera 200 is shown.For clarity, only the components necessary to explain the embodiments ofthe invention are shown. The lens 100 includes the focus lens 102 andthe zoom lens group 104, which are substantially aligned along theoptical axis 110. In one embodiment, the zoom lens group 104 includes afirst zoom lens 106 and a second zoom lens 108. The focus lens 102 mayinclude one or more separate optical elements. The first zoom lens 106and the second zoom lens 108 each may include one or more separateoptical elements. An image detector 130 is located substantially on theoptical axis 110, on the opposite side of the focus lens 102 from thezoom lens group 104, such that an image may be focused on the imagedetector 130 by the focus lens 102. In one embodiment, the imagedetector 130 is a CCD, but the image detector 130 maybe another devicesuch as a metal-oxide semiconductor, or may be photographic film. Thelens 100 of the camera 200 collects light that passes along the opticalaxis 110 through the zoom lens group 104 and the focus lens 102 beforeit is focused onto the image detector 130.

[0019] The focus lens 102 is operably connected to a stepper motor 202controlled by a motor driver 204, which in turn is electricallyconnected to a controller 206. A motor driver 204 is a standardelectrical component used to drive a stepper motor 202, and controls themotor 202 to ensure that it moves in discrete, substantially equalsteps. The stepper motor 202 moves the focus lens 102 in discrete stepssubstantially along the optical axis 110, based on commands issued bythe controller 206. In other embodiments, a motor other than a steppermotor 202 may be used.

[0020] The controller 206 may be an application-specific integratedcircuit (ASIC), a microprocessor, or any other information handlingdevice adapted to control the focus lens 102. The controller 206controls the focus lens 102 to automatically focus the camera 200.Automatically focusing a camera utilizing a controller 206 is standardin the art, and may be performed in a number of different standard ways.The controller 206 is connected to a memory storage unit 210. In oneembodiment, the memory storage unit 210 is random-access memory (RAM),but may be any other memory storage device, such as flash memory.

[0021] In one embodiment, the controller 206 is also connected to asensor 208. The sensor 208 senses when the focus lens 102 is in aparticular reference position, which may be referred to as the homeposition. When the sensor 208 is in the home position, it transmits asignal to the controller 206. The controller 206 then preferably storesin a memory storage unit 210 the information that the focus lens 102 isin the home position. In one embodiment, the position of the focus lens102 is a register or combination of registers in the memory storage unit210, where the position of the focus lens 102 is stored as zero when thefocus lens 102 is in the home position. The stepper motor 202 and themotor driver 204 act both to move the focus lens 102 and measure itscurrent position. The focus lens 102 is initialized in the homeposition, at which point the sensor 208 signals the controller 206 thatthe focus lens is located in the home position. That position is storedin the memory storage unit 210. As the stepper motor 202 moves the focuslens 102 in discrete increments in one direction along the optical axis110, the controller 206 increments the focus lens position stored in thememory storage unit 210 one unit for each discrete increment. In oneembodiment, the controller 206 increments the focus lens position storedin the memory storage unit 210 substantially at the same time as ittransmits a command to the stepper motor 202 via the motor driver 204 tomove one discrete increment in one direction away from the homeposition. Similarly, the controller 206 decrements the focus lensposition stored in the memory storage unit 210 substantially at the sametime as it transmits a command to the stepper motor 202 via the motordriver 204 to move one discrete increment in the opposite directiontoward the home position. The position of the focus lens 102 along theoptical axis 110 at any point in time can then be determined by thecontroller 206 by reading the focus lens position data stored in thememory storage unit 210.

[0022] The lenses 106, 108 forming the zoom lens group 104 are movablesubstantially along the optical axis 110. In one embodiment, the lenses106, 108 of the zoom lens group 104 are connected to a rotating lensbarrel cam mechanism 212, which is standard in the art. The rotatinglens barrel cam mechanism 212 provides for motion of the lenses 106, 108substantially along the optical axis 110, and in one embodiment providesfor substantially equal linear displacement of each lens 106, 108 alongthe optical axis when the zoom lens group 104 is moved, to provide forsmooth motion among a variety of magnification settings. The particularmechanical implementation of the rotating lens barrel cam mechanism 212is not critical.

[0023] A DC motor 214 is connected to rotating lens barrel cam mechanism212. In one embodiment, the DC motor 214 drives the motion of therotating lens barrel cam mechanism 212 via a set of gears between the DCmotor 214 and the rotating lens barrel cam mechanism 212. However, othermechanical interfaces between the DC motor 214 and the rotating lensbarrel cam mechanism 212 may be used, if desired. Further, anotherdevice than the DC motor 214 may be used to drive the rotating lensbarrel cam mechanism 212.

[0024] In one embodiment, the rotating lens barrel cam mechanism 212 ismechanically connected to a slide potentiometer 220, which in turn isconnected to the controller 206. The slide potentiometer 220 is astandard component that measures the position of the lenses 106, 108along the optical axis 110 and provides feedback about that measuredposition to the controller 206 for controlling the motion of the lenses106, 108. In one embodiment, the slide potentiometer 220 includes amechanical slide component mechanically connected to the rotating lensbarrel cam mechanism 212 via one or more gears, and provides a variableresistance depending on the position of that mechanical slide. However,another type of position feedback device, such as a motor shaft encoderor a linear optical encoder, may be used to sense and control the motionof the zoom lens group 104.

[0025] A motor driver 222 is standard in the art, and is connected tothe DC motor 214 in one embodiment. The controller 206 moves the zoomlens group 104 by transmitting a signal to the motor driver 222, whichthen provides a corresponding current to the DC motor 214, causing it tomove the rotating lens barrel cam mechanism 212, which in turn moves thezoom lens group 104. The setting of the slide potentiometer 220 changesas a result, changing the resistance of the slide potentiometer 220 toreflect the new position of the rotating lens barrel cam mechanism 212.Because the resistance of the slide potentiometer 220 varies with theposition of the slide, and each position of the slide in the slidepotentiometer 220 corresponds to a particular position of the lenses106, 108, the controller 206 can determine the position of the lenses106, 108 at any point in time by sensing the resistance of the slidepotentiometer 220.

[0026] A zoom control 216 is a control accessible to a user of thecamera 200, and may be a rocker switch, touch switch, or any otherdevice capable of recognizing user input. The particular configurationof the zoom control 216 is not critical to the invention. The zoomcontrol 216 is connected to the controller 206, such that the controller206 can adjust the zoom lens group 104 based on user input receivedthrough the zoom control 216.

[0027] A focus control 224 is a control on the camera 200 accessible toa user, through which the user controls the autofocus function of thecamera. In one embodiment, the focus control 224 is the shutter button(not shown), where the depression of the shutter button to a firstposition allows the user to initiate the autofocus function. Theinstigation of an autofocus function upon the partial depression of ashutter button to a first position is standard. In another embodiment,the focus control 224 may be a separate rocker switch, touch switch, orany other device capable of recognizing user input. The particularconfiguration of the focus control 224 is not critical to the invention.

[0028] Similarly, a macro control 218 may be provided on the camera 200,where the macro control 218 is accessible to a user of the camera 200,through which the user controls the macro function for closeup focusing.The macro control 218 is connected to the controller 206, such that thecontroller 206 can adjust the focus lens 102 based on user inputreceived through the macro control 218. The focus lens 102 can movethrough a range of positions close to the front focusing position 122,including the front focusing position 112, when the user selects themacro function via the macro control 218. In another embodiment, themacro control 218 is used to position the focus lens 102 in a closeupfocusing position near the front focusing position 122. In anotherembodiment, the macro control 218 is not used, and the camera 200 senseswhen an object is close enough for macro focusing, as a part of itsstandard autofocus function. The autofocus function of a camera isstandard in the art, and may be implemented in any manner in the camera200. The particular implementation of the autofocus function, whether inhardware, software or a combination of both, is not critical.

[0029] Referring to FIG. 3, a method 300 for focus control in a camera200 is shown. The method 300 is utilized where a particular setting ofthe zoom lens group 104 has been chosen, and the focus distance changes.This situation occurs where a particular magnification setting has beenselected with the zoom control 216, after which the user selects adifferent object for imaging at a different distance from the camera.For example, the user may select wide-angle magnification with regard toa person standing close to the camera, then move the camera to focusupon a building in the distance without changing the magnification.

[0030] First, in block 302, the controller 206 receives input to changethe focus distance of the focal lens 102. This input may be received inat least two different ways. First, the user may instruct the camera 200to autofocus on a subject. In one embodiment, this is performed bydepressing the shutter button on the camera 200 to a first position. Theuser may utilize the macro control 218 to transmit input to the iscontroller 206 indicating that the subject to be focused upon is closeto the camera 200. Second, the user may simply move the camera to focuson a different object, such that the autofocus function of the camera200 transmits information to the controller 206 to change the focusdistance of the focus lens 102. Other sources of input may be used ifdesired. For example, if the lens 100 is associated with a web-enabledcamera that is located remotely from the user, the user may transmit asignal from an information handling system to the web-enabled cameraover a communications network, where that signal is related to thecontrol of the focus lens 102. That signal input is received by thecontroller 206.

[0031] Next, in block 304, the controller 206 determines the position ofthe zoom lenses 106, 108. As described above, in one embodiment thecontroller 206 determines the position of the lenses 106, 108 bychecking the resistance of the slide potentiometer 220. The controller206 may do so by applying a voltage to the slide potentiometer 220, thenmeasuring the current that flows through the slide potentiometer 220.Because the resistance of the slide potentiometer 220 varies with theposition of the slide, and each position of the slide in the slidepotentiometer 220 corresponds to a particular position of the lenses106, 108, the controller 206 can determine the position of the lenses106, 108 at any point in time by checking the resistance of the slidepotentiometer 220. The controller 206 may store this position data inthe memory storage unit 210 or in a cache within the controller 206, ifdesired.

[0032] Next, in block 306, the controller 206 determines the permissibleworking range of the focus lens 102, based on the position of the zoomlenses 106, 108 determined in block 304. The permissible working rangeis the range of possible positions of the focus lens 102 along theoptical axis 110 within which the focus lens 102 does not approachcloser than a minimum safe distance to the second zoom lens 108. Theminimum safe distance is a distance chosen to provide a margin of safetybetween the lenses 102, 108 and prevent their collision. In oneembodiment, the minimum safe distance is substantially five millimeters.By defining a permissible working range, the focus lens 102 can beprevented from colliding with the second zoom lens 108 as the focus lens102 is moved to a focus position. In one embodiment, the controller 206determines the position of the front boundary of the permissible workingrange by subtracting the minimum safe distance from the position of thesecond zoom lens 108 determined in block 304. In such an embodiment, thepositions of the lenses 102, 106, 108 are measured along the opticalaxis 110, where the zero point corresponds to the rear focusing position120, and position information is measured in positive numbers extendingforward along the optical axis 110 from the rear focusing position 120.Other coordinate systems and methods of measuring are possible. In oneembodiment, the rear boundary of the permissible working range is therear focusing position 120.

[0033] Next, in block 308, the controller 206 moves the focus lens 102to the best focus position within the permissible working range, whichmay or may not be the same position as the absolute best position forthe focus lens 102. In one embodiment, the best focus position withinthe permissible working range is determined using an iterative process,where the focus lens 102 is moved in discrete steps based on the valueat each step of a focus figure of merit (FOM). The use of a focus FOM isstandard. In one embodiment, the focus FOM is a measure of imagecontrast as sensed by, for example, the image detector 130. Focus istypically related to contrast, such that the contrast is higher as thefocus improves. In one embodiment, standard dedicated hardware is usedto compute the focus FOM from image contrast sensed by the imagedetector 130. In another embodiment, standard circuitry in thecontroller 206 is used to compute the focus FOM from image contrastsensed by the image detector 130. Other bases for a focus FOM may beused, if desired.

[0034] To move the focus lens 102 to the best focus position within thepermissible working range, the focus lens 102 is moved within thepermissible working range until a position of the focus lens 102 isreached where the focus FOM is maximized. The best focus position withinthe permissible working range may not be the same as the absolute bestfocus position absent the constraint of the permissible working range.As one example, if the absolute best position for the focus lens 102falls in front of the front boundary of the permissible working range,the best position for the focus lens 102 in the permissible workingrange is the front boundary of that permissible working range. Thus, thefocus lens 102 can be moved as close as possible to the absolute bestfocus distance without damaging the second zoom lens 108.

[0035] In one embodiment, a peak finding algorithm is used to move thefocus lens 102. The position of the focus lens 102 is tracked as it ismoved. In one embodiment, the controller 206 checks the initial positionof the focus lens 102 by reading position data from the memory storageunit 210, where that position data is stored in the memory storage unit210 as described above. The controller 206 may determine the initialposition of the focus lens 102 in other ways, if desired. Next, thefocus lens 102 is moved in a direction along the optical axis 110 by thestepper motor 202 in conjunction with commanded moves to the steppermotor driver 204,which in turn is controlled by the controller 206. Thecontroller 206 tracks the position of the focus lens 102 by updatingfocus lens 102 position data within the memory storage unit 210 inconjunction with the motion commands transmitted to the stepper motor202 via the stepper motor driver 204, such that the new position of thefocus lens 102 is stored in the memory storage unit 210. Next, it isdetermined whether the focus FOM has increased or decreased from theinitial position of the focus lens. If the focus FOM has increased, thenthe focus lens 102 is moved again in that direction until a peak isfound or a boundary of the permissible working range is reached. If thefocus FOM has decreased, then the focus lens 102 is moved again in theopposite direction, until a peak is found or a boundary of thepermissible working range is reached. As above, the focus lens 102 ismoved in discrete steps, and its position at each step is tracked by thecontroller 206. When the focus lens 102 has reached a location on theoptical axis substantially at a peak focus FOM, or when the focus lens102 reaches a boundary of the permissible working range, the controller206 stops the focus lens 102 at a final focus lens 102 position. Asdescribed above, the focus lens 102 is moved in discrete steps and itsposition is tracked by the controller 206.

[0036] Because the stepper motor 202 moves the focus lens 102 indiscrete steps, the best focus position within the permissible workingrange may not correspond precisely to a position into which the focuslens 102 can be placed. If so, the controller 206 controls the steppermotor 202 to move the focus lens 102 into the discrete position closestto the best position within the permissible working range, whileensuring that the focus lens 102 does not move out of the permissibleworking range. Next, in block 310, the controller 206 saves the finalfocus lens 102 position, and additionally saves the associated focusdistance. The method 300 then ends at block 312.

[0037] Referring to FIG. 4, a method 400 for zoom control in a camera200 is shown. The method 400 is utilized where a particular focussetting of the focus lens 102 has been chosen, and the magnificationchanges. This situation occurs where a particular focus setting has beenset by the controller 206 or selected with the macro control 218, afterwhich the magnification selected with the zoom control 216 camera 200 ischanged to zoom in on an object or zoom out from an object. For example,the user may focus on a flower close to the camera with the macrocontrol 218, then select a higher degree of magnification with the zoomcontrol 216 to better view the details of the flower.

[0038] First, in block 402, the controller 206 receives input to changethe magnification of the zoom lens group 104. In one embodiment, theuser utilizes the zoom control 218 to change magnification, where thezoom control 216 transmits input to the controller 206. Other sources ofinput may be used if desired. For example, if the lens 100 is associatedwith a web-enabled camera that is located remotely from the user, theuser may transmit a signal from an information handling system to theweb-enabled camera over a communications network, where that signal isrelated to the control of the zoom lens group 104. That signal input isreceived by the controller 206.

[0039] Next, in block 404, the controller 206 determines the position ofthe focus lens 102 and the focal distance. In one embodiment, thecontroller 206 checks the position of the focus lens 102 by readingposition data from the memory storage unit 210, where that position datais stored in the memory storage unit 210 as described above.

[0040] The controller 206 may determine the position of the focus lens102 in other ways, if desired.

[0041] Next, in block 406, the controller 206 determines the initialposition of the zoom lenses 106, 108. As described above, in oneembodiment the controller 206 determines the position of the lenses 106,108 by checking the resistance of the slide potentiometer 220. Thecontroller 206 may do so by applying a voltage to the slidepotentiometer 220, then measuring the current that flows through theslide potentiometer 220. Because the resistance of the slidepotentiometer 220 varies with the position of the slide, and eachposition of the slide in the slide potentiometer 220 corresponds to aparticular position of the lenses 106, 108, the controller 206 candetermine the position of the lenses 106, 108 at any point in time bychecking the resistance of the slide potentiometer 220. The controller206 may store this position data in the memory storage unit 210 orwithin a cache within the controller 206, if desired.

[0042] Next, in block 408, the controller 206 moves the zoom lens group104 a discrete distance along the optical axis 110 in the directioncorresponding to the magnification selected by the input received inblock 402. The controller 206 moves the zoom lens group 104 as describedabove, by transmitting a signal to the motor driver 222, which in turndrives the DC motor 214 that moves the rotating lens barrel cammechanism 212 connected to the zoom lens group 104.

[0043] Next, in block 410, the controller 206 moves the focus lens 102to the best focus position within the permissible working range thatachieves focus for the original focus distance at the new position ofthe zoom lens group 104. In one embodiment, block 410 is performed in amanner as disclosed in the copending United States patent applicationentitled “Brightness Control for Auto-Focus in an Optical System” (HPDocket No. 10006923-1), naming Gregory V. Hofer, David K. Campbell,Masahiro Ohno, and Yoshihiro Yamazaki as inventors and filed on evendate herewith.

[0044] Next, in block 412, the controller 206 determines if additionalmotion of the zoom lens 104 is required. In one embodiment, thecontroller 206 makes this determination by checking the zoom control 218to determine if the user continues to select a change in magnification.If an additional change to the magnification is required, the method 400returns to block 406. However, if no additional change in magnificationis required, the method 400 ends at block 414.

[0045] Referring to FIG. 5, an exemplary configuration of the lens 100in block 318 is shown. In this example, the user is taking a telephotophotograph of a distant object, such that the object may be consideredto be at infinity. Thus, the focus lens 102 is at the rear focusingposition 120. As described above, in block 318 the lens 100 isconfigured for telephoto imaging, after receiving user input to zoom inon an object. To configure the zoom lens group 104 for a telephotoimage, the first zoom lens 106 and the second zoom lens 108 are movedrelatively close to one another along the optical axis 110, where thesecond zoom lens 108 is separated from the focus lens 102 by asubstantial distance along the optical axis 110. The minimum safedistance 500 from both the second zoom lens 108 and the focus lens 102is shown, thereby showing that the second zoom lens 108 and the focuslens 102 are further away from each other than the minimum safe distance500.

[0046] Referring to FIG. 6, an exemplary configuration of the lens 100in step 320 is shown. In this example, the user is taking a wide anglephotograph of a close-up object at macro focusing distance. Thus, thefocus lens 102 is at the front focusing position 122. As describedabove, in block 320 the lens 100 is configured for wide angle imaging,after receiving user input to zoom out from an object. The zoom lensgroup 104 is set for a wide angle image, such that the first zoom lens106 and the second zoom lens 108 are relatively far apart from oneanother along the optical axis 110. To configure the zoom lens group 104for a wide-angle image, the lenses 106, 108 of the zoom lens group 104are moved relatively further from each other along the optical axis,such that the second zoom lens 108 approaches the focus lens 102 in thefront focusing position 122. As the second zoom lens 108 approaches thefocus lens 102, the second zoom lens 108 is stopped by the controller206 at the minimum safe distance 500 from the focus lens 102, so thatthe second zoom lens 108 is not moved all the way to the rear zoomposition 126. In this way, the method 300 prevented the second zoom lens108 from colliding with the focus lens 102.

[0047] Referring to FIG. 7, a power-off position of the zoom lens group104 and the focus lens 102 is shown. The power-off position is theposition to which the zoom lens group 104 and the focus lens 102 aremoved as the camera 200 is shut down. The focus lens 102 is moved alongthe optical axis 110 to a home position, which is the closestpermissible position to the image detector 130. In one embodiment, thehome position of the focus lens 102 is the rear focusing position 120.However, the home position of the focus lens 102 may be located betweenthe rear focusing position 120 and the image detector 130. The homeposition of the focus lens 102 is chosen to ensure that the focus lens102 does not inadvertently collide with the image detector 130, becausesuch a collision may damage either or both of those components. In thepower-off position, the zoom lens group 104 is also moved back along theoptical axis 110 to a position near the focus lens 102. In FIG. 7, thehome position of the focus lens 102 is equivalent to the rear focusingposition 120, such that the second zoom lens retracted position 700 islocated substantially at the minimum safe distance 500 from the rearfocusing position 120.

[0048] Referring to FIG. 8, a method 800 for moving the lens 100 to thepower-off position is shown. In block 802, the controller 206 receives arequest to power down the camera 200. In one embodiment, such a requestis received from a power switch (not shown) on the camera 200, which isdepressed or otherwise activated by a user when the user wishes to turnoff the camera 200.

[0049] In response to the request received in block 802, in block 804the controller 206 moves the focus lens 102 to the home position. Asdescribed above, the home position is located along the optical axis 110at the closest permissible distance to the image detector 130. In oneembodiment, the home position is the same as the rear focusing position120. The controller 206 moves the focus lens 102 as described above, bytransmitting a command to the stepper motor driver 204, which in turndrives the stepper motor 202 to move the focus lens 102 to the closestpermissible position to the image detector 130, as commanded. The zoomlens group 104 is held stationary during block 804.

[0050] Next, in block 806, the zoom lens group 104 is moved to apower-off position, which may also be referred to as a retractedposition. As described above, the power-off position of the zoom lensgroup 104 is the position where the second zoom lens 108 is positionedat a second zoom lens retracted position 700, located no closer than theminimum safe distance 500 from the home position of the focus lens 102.The zoom lens group 104 is moved to the power-off position by a commandtransmitted from the controller 206 to the motor driver 222, which inturn drives the DC motor 214 to move the rotating lens barrel cammechanism 212. The zoom lens group 104 is thus moved to the power-offposition, where the second zoom lens 108 is at the second zoom lensretracted position 700. In one embodiment, the second zoom lensretracted position 700 is permanently stored in the controller 206 orthe memory storage unit 210. However, the second zoom lens retractedposition 700 may be calculated in block 806, if desired. By moving thefocus lens 102 to its home position before moving the zoom lens group104 to its power-off position, and by moving the second zoom lens 108 nocloser than the minimum safe distance 500 to the focus lens 102,collisions between the focus lens 102 and the second zoom lens 108 areprevented.

[0051] While the embodiments above have been described in terms ofcomponents of a camera 200, the method 300 may be practiced with otheroptical image acquisition devices, such as binoculars, telescopes,spotting scopes, or other optical devices.

[0052] Although the invention has been described with reference toparticular embodiments, the description is only an example of theinvention's application and should not be taken as a limitation.Consequently, various adaptations and combinations of features of theembodiments disclosed are within the scope of the invention as definedby the following claims and their legal equivalents.

What is claimed is:
 1. A method for controlling a lens group having afocus lens and a zoom lens group along an optical axis, where the zoomlens group includes at least one zoom lens, comprising: receiving inputto change the position of a selected one of the focus lens and the zoomlens group; and separately controlling the positions of the focus lensand the zoom lens group along the optical axis such that the focus lensand the second zoom lens approach substantially no closer to one anotherthan a selected minimum safe distance.
 2. The method of claim 1, whereinsaid receiving comprises receiving input to change the position of thefocus lens.
 3. The method of claim 2, wherein said separatelycontrolling comprises determining the initial position of the at leastone zoom lens.
 4. The method of claim 2, wherein said separatelycontrolling comprises determining a permissible working range.
 5. Themethod of claim 4, wherein said determining a permissible working rangeis performed by subtracting a minimum safe distance from said initialposition of the at least one zoom lens.
 6. The method of claim 4,further comprising moving the focus lens to the best focus positionwithin said permissible working range.
 7. The method of claim 6, whereinsaid moving the focus lens to the best focus position within saidpermissible working range comprises: selecting a focus figure of merit;moving the focus lens in one direction along the optical axis; trackingthe position of the focus lens along the optical axis; if the focusfigure of merit increases, moving the focus lens again in said onedirection to a final position, said moving performed no further than aboundary of said permissible working range; and if the focus figure ofmerit decreases, moving the focus lens again in a direction oppositesaid one direction to a final position, said moving performed no furtherthan a boundary of said permissible working range
 8. The method of claim7, wherein said final position substantially corresponds to a positionon the optical axis where a peak value of said focus figure of merit isreached.
 9. The method of claim 7, wherein said final position is aboundary of said permissible working range.
 10. The method of claim 1,wherein said receiving comprises receiving input to change the positionof the zoom lens group.
 11. The method of claim 10, wherein saidseparately controlling comprises determining the initial position of thefocus lens and the focal distance associated with said initial position.12. The method of claim 10, wherein said separately controllingcomprises determining the initial position of at least one zoom lens.13. The method of claim 12, further comprising moving at least one zoomlens a discrete amount along the optical axis to a new position in thedirection associated with said received input.
 14. The method of claim13, further comprising: determining a permissible working range alongthe optical axis; and moving the focus lens to the best focus positionwithin said permissible working range, wherein the best focus positionwithin said permissible working range achieves focus for said initialfocal distance at said new position of said at least one zoom lens. 15.The method of claim 14, further comprising repeating said said movingthe second zoom lens, said determining a permissible working range, andsaid moving the focus lens until at least one zoom lens has reached afinal position associated with said received input.
 16. The method ofclaim 1, wherein said receiving comprises receiving input to move thelens group to a power-off position.
 17. The method of claim 16, whereinsaid separately controlling comprises: moving the focus lens to a homeposition; and moving the zoom lens group such that the second zoom lensmoves to a second zoom lens retracted position, said moving the zoomlens group performed after said moving the focus lens, wherein saidsecond zoom lens retracted position is substantially at a minimum safedistance from the home position along the optical axis.
 18. A method forcontrolling a lens group having a focus lens and a zoom lens group alongan optical axis, where the zoom lens group has a first zoom lens and asecond zoom lens, comprising: receiving input to change the position ofthe focus lens; determining the initial position of the second zoomlens; determining a permissible working range by subtracting a minimumsafe distance from said initial position of said second zoom lens;selecting a focus figure of merit; moving the focus lens in onedirection along the optical axis; tracking the position of the focuslens along the optical axis; if the focus figure of merit increases,moving the focus lens again in said one direction to a final position,said moving performed no further than a boundary of said permissibleworking range; and if the focus figure of merit decreases, moving thefocus lens again in a direction opposite said one direction to a finalposition, said moving performed no further than a boundary of saidpermissible working range.
 19. A method for controlling a lens grouphaving a focus lens and a zoom lens group along an optical axis, wherethe zoom lens group has a first zoom lens and a second zoom lens,comprising: receiving input to change the position of the zoom lensgroup; and determining the initial position of the focus lens and thefocal distance associated with said initial position; determining theinitial position of the second zoom lens; moving the second zoom lens adiscrete amount along the optical axis to a new position in thedirection associated with said received input; determining a permissibleworking range along the optical axis; moving the focus lens to the bestfocus position within said permissible working range, wherein the bestfocus position within said permissible working range achieves focus forsaid initial focus distance at said new position of said second zoomlens; and repeating said moving the second zoom lens, said determining apermissible working range and said moving the focus lens until thesecond zoom lens has reached a final position associated with saidreceived input.